1. Field of the Invention
The present invention relates to an apparatus for controlling a gear type automatic transmission, and in particular, to an improvement in the speed of response of an automatic transmission provided with a clutch. Furthermore, the present invention relates to a technique for stopping a vehicle smoothly during idle-up control. Moreover, the present invention especially relates to a technique for eliminating batting states of a synchromesh mechanism in a sub transmission, in a gear change control device of a multi-stage transmission in which the sub transmission is connected to the output side of a main transmission.
2. Description of the Related Art
In recent years, mechanical automatic transmissions have been utilized that change gears automatically according to running conditions, by electronically controlling a friction clutch and a gear type transmission. In a mechanical automatic transmission, since there is no fluid clutch (torque converter) in the driving force transfer system from the engine to the driving wheels, the driving force transfer efficiency is high, and hence it is possible to improve fuel consumption. Furthermore, since there is no slipping sensation which is unique to a fluid clutch, the drivability is also improved.
In a gear type transmission, after the gear is changed to the neutral position, the driving force is disconnected from the engine. Therefore, in a mechanical automatic transmission, when stopping a vehicle from the drive stage, control is typically performed for engaging a friction clutch after changing the gear type transmission to the neutral position. Furthermore, in gear change control of a mechanical automatic transmission, as disclosed in Japanese Unexamined Patent Publication No. 2001-227630, and a prior application (Japanese Patent Application No. 2001-92119) by the present applicant, a technique is proposed in which when a gear type transmission is changed to the neutral position but immediately before the vehicle is stopped, an acceleration operation is performed in order to reaccelerate, the transmission is changed to an optimum gear according to the vehicle speed.
However, in a mechanical automatic transmission, the friction clutch is disengaged and engaged using an actuator. Therefore, at the time when the vehicle should be stopped, if when the gear type transmission is changed to the neutral position and the friction clutch is engaged, then even if an acceleration operation is performed in order to reaccelerate, the friction clutch needs to be disengaged again in order to change the gear. Hence the speed of response is not satisfactory.
Therefore, taking the above-described existing problems into consideration, the present invention makes it an object thereof to provide an apparatus for controlling an automatic transmission that does not require the friction clutch to be disengaged at the time of reacceleration, by maintaining a state in which the friction clutch is disengaged after a gear type transmission is changed to the neutral position when stopping a vehicle from the drive stage, so that the speed of response is improved.
On the other hand, a vehicle engine is provided with an idle-up device in order to stabilize the engine rotation during the time that the water temperature is low, and to complete warming up quickly. For the idle-up device, there is a manual idle-up device that increases the engine rotational speed at the time of idling by the driver controlling the idle volume, and an automatic idle-up device that increases the engine rotational speed at the time of idling up to a predetermined value (idle-up rotational speed) automatically depending on the temperature of the cooling water. Using these idle-up devices, the amount of fuel supplied is controlled so as to maintain the idle-up rotational speed, and hence the engine rotational speed is maintained almost constant as the workload changes.
Accordingly, in a vehicle in which an idle-up device and a mechanical automatic transmission as described above are provided, in the case where the idle-up rotational speed is set to be greater than the rotational speed at which changing to the neutral position takes place, when idle-up control is performed, even if the driver operates the brake in order to stop the vehicle from the drive stage, the engine rotational speed does not become less than or equal to the rotational speed at which changing to the neutral position takes place, and the gear type transmission does not go into the neutral position.
Accordingly, it is necessary for the driver to press the brake pedal down more strongly than necessary in order to force the engine rotational speed to drop, so that the engine rotational speed drops to become less than the rotational speed at which changing to the neutral position takes place, and the gear type transmission is set to the neutral position. By so doing, the sensation of operating the brake becomes unpleasant. Furthermore, there is a possibility that the load on the brake increases more than needed.
Therefore, taking the above-described existing problem into consideration, the present invention makes it an object thereof to provide an apparatus for controlling a mechanical automatic transmission that, in a vehicle provided with an idle-up device, determines that an engine is in an idle-up state based on the engine torque, when stopping the vehicle from the drive stage, and changes the gear to the neutral position, so that the vehicle stops smoothly.
While, in a tractor that pulls a trailer, since the weight of the vehicle is great, a multi-stage transmission is often installed in order to improve the running performance. In recent years, a type is becoming mainstream in which part of the gear train of the main transmission is shared by connecting a sub transmission to a main transmission in series, in order to achieve miniaturization. Furthermore, a technique has been also proposed that realizes an efficient automatic transmission by controlling a mechanical clutch and a multi-stage transmission electronically (refer to Japanese Unexamined Patent Publication No. 2001-165294).
For example, an example of a multi-stage transmission is one in which a splitter and a range are linked to a main transmission on its input side and output side respectively as sub transmissions, each gear of the main transmission is shifted by a half stage, and the gear ratio is expanded to multiple stages. In such a multi-stage transmission, in order to reduce the load on the synchromesh mechanism (inertia on the synchronizing side) in the range, gear change control is performed in which the range is changed when the main transmission is in its neutral, and after the range change is completed, the main transmission is changed to a predetermined gear.
Incidentally, in the case where the synchronizing side and the side to be synchronized are stopped completely in a typical synchromesh mechanism, there is a possibility that a “batting state” occurs, in which the chamfered ends of a synchronizer sleeve and a synchronizer ring interfere. If a batting state occurs, the synchronizer sleeve cannot slide in the direction of a gear on the side to be synchronized, so that the gear cannot be changed. Although the frequency of batting states occurring is reduced due to improvement of the chamfered end shape of the synchronizer sleeve and the synchronizer ring, it cannot be avoided reliably at present.
When the main transmission is set to the neutral position and the clutch is engaged, since relative rotation occurs between the main gear and the main shaft, the positional relationship between the chamfered ends of the synchronizer sleeve and the synchronizer ring changes, so that the batting state of the main transmission can be avoided easily.
However, in a multi-stage transmission, since the main transmission is changed after the range change is completed, if a batting state occurs in the range, changing of the main transmission cannot be started. Accordingly, since the main gear and the main shaft do not engage, even if the clutch is engaged, the main shaft does not rotate. Therefore, it is not possible to generate relative rotation between the main shaft and the range gear. Accordingly, when a batting state occurs in the range, then for example the vehicle must depart slowly while maintaining the range in a high speed gear in order to change the range.
While the vehicle is stopped, the main transmission is in the neutral position most of the time. Furthermore, when the vehicle stops from normal driving, there are many cases where the range is changed to a high speed gear. Accordingly, when the vehicle starts moving, there is a high possibility that the range must be changed from the high speed gear to the low speed gear in a state in which the main gear, the main shaft, and the range gear are not rotating, so problems as described above occur easily.
Therefore, taking the above-described existing problems into consideration, the present invention makes it an object thereof to provide a gear change control apparatus of a multi-stage transmission that, in a multi-stage transmission in which a sub transmission is connected to an output side of a main transmission, eliminates batting states of the synchromesh mechanism in the sub transmission by changing the content of the gear change control.